Radio Sounding of the Near-Sun Plasma Using Polarized Pulsar Pulses


НазваRadio Sounding of the Near-Sun Plasma Using Polarized Pulsar Pulses
Дата конвертації06.06.2013
Розмір445 b.
ТипПрезентации


Radio Sounding of the Near-Sun Plasma Using Polarized Pulsar Pulses

    • I.V.Chashei, T.V.Smirnova, V.I.Shishov
  • Pushchino Radio Astronomy Obsertvatory, Astrospace Center, Lebedev Physical Institute


ABSTRACT



Propagation effects of pulsed signals in the solar wind

  • Dispersion delay of pulses

  • Scattering of pulses on electron density fluctuations

  • Faraday rotation of polarization plane



Dispersion delay of pulses

  • t = A 2  DM , A = const

  • DM =  N dz



Scattering of pulses on electron density fluctuations

  • Structure function of radio wave phase fluctuations

  • DS() =2(re)2 <Nl2(R0)> (/l)2 lReff

  • l – turbulence inner scale

  • Wave field coherence scale 0

  • DS(0) = 1

  • Scattering angle sc

  • sc =  / 2 0

  • Pulse broadening by scattering

  • sc = z sc2 / 2 c



Scattering of pulses on electron density fluctuations

  • t

  • I(t) = I0 exp ( - t2 / 02 ) exp [( t - t) / sc ] dt

  • -

  • I(t) = I0 exp (02/4 sc2 – t/ sc) [ 1 -  (0/2 sc – t/ 0 ) ]

  • Max. at t  0



Faraday rotation of polarization plane

  •  = C  2  RM , C = const

  • RM =  N Bz dz



Observations

  • Radio telescope BSA LPI : geometric area 70 000 м2,

  • operation frequency 111 МHz

  • Receiver: 96 channels  20 кГц, whole bandwidth 1.92 МHz, integration time 2.68 мs

  • Pulsar В 0525+21: period 3,74 s, two components, polarization degree 40-50 %; yy 2005, 2007.

  • Pulsar in the Crab nebula В 0531+21: period 33 мs, giant pulses, polarization degree10 % ; y 2007 .







Pulsars coronal occultation



Example of pulsar В 0525 record



Dispersion delay for pulsar PSR В 0525, 2005, 2007



Pulse delay and ambient plasma density

  • Dispersion delay upper estimate :

  • t < 2 ms  DM < 2  1016 cm-2 

  • N (5.5 R) < 2 104 cm-3 (2005)

  • t < 4 ms  DM < 4  1016 cm-2 

  • N (5.5 R) < 4 104 cm-3 (2007)

  • Counselman & Rankin, 1969-1970 observations , 111-430 Мгц :

  • t  5 ms, N (10 R)  7 103 cm-3, N (5.5 R)  6 104 cm-3



Dispersion delay for PRS B 0531, 2007



Density dependence on the distance from the Sun, PSR B 0531, 2007



Giant pulses of PSR В 0531



PSR В 0531scattering



Scattering and density fluctuations

  • Upper estimate of pulse broadening (B 0531):

  • sc < 2 ms  scattering angle sc < 3 10-3 rad  10

  • Counselman & Rankin, 1969-1970 observations, 111-430 МHz :

  • sc  6 ms



PSR В 0525 Faraday rotation



Rotation measure radial profile В 0525



Rotation measure

  • Rotation measure upper estimate at R = 7 R :

  • RM < 6 rad/m2 (2005 y.)

  • RM < 3 rad/m2 (2007 y.)

  • Bird et al., observations 1978-1979 y.: RM < 10 rad/m2



Conclusions

  • Our estimates of t, sc show, that in the years 2005-2007 mean density, as well density fluctuations were several times (2-3) lower, than in observations 1969-1970 г. (Counselman & Rankin).

  • During period of closest approach solar offset point of radio path was located at high heliolatitudes, about 80о. Possible explanation: polar coronal hole with low plasma density at solar activity minimum.

  • Our estimates of rotation measure are in agreement with the results of Bird et al., (1978-1979г.). The deviations in spatial magnetic field distribution from spherically symmetric are modest: Bns < 610-3 G, Br> 210-2 G .

  • Radial density profile ( B 0531, 2007) show that the acceleration of fast solar wind continues up to the distances about 5 – 10 RS .



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